In Spike Jonze's new sci-fi romance, Her, Joaquin Phoenix plays a divorcé who rebounds by falling in love with his smartphone. On a recent Wednesday, however, he's a delinquent boyfriend, leaving his iPad abandoned on a chair in a Lebanese restaurant in L.A. as he bounces off to the parking lot for a smoke. After a few puffs, he reconsiders and darts back inside, lest the well-dressed ladies at the next table snatch it to pay for a month of hummus.

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"They said they were going to steal it!" Phoenix yelps. "I thought they looked nice!"

Back in his seat, he spins around and points, "What is that, by the way?" When the two women duly pivot, he steals the blond's purse. "Classic move! Classic move!" he teases them. "C'mon guys, we're all playing here."

It's unclear if his victims even know they're tangling with the three-time Oscar-nominated star of Gladiator, Walk the Line and The Master as well as the upcoming Her, which has been racking up awards on its way to an all-but-inevitable Best Picture nomination.

Although the 39-year-old actor is famous for playing hotheads, in person he's a goof. Phoenix is one of the major talents of his generation, but he'd rather gush about DJ Premier ("He's such an amazing artist!") than tout his own creative process. In his black jeans and gray-streaked, shoulder-length hair, he looks more like a struggling grunge guitarist than a reluctant red-carpet walker who's all too familiar with tuxedos.

The ladies giggle nervously, not sure if they've been punked. But they have definitely been Phoenixed — flummoxed and fascinated by this charismatic joker.

We've all been Phoenixed. Five years ago, with still-fresh accolades from Walk the Line and a fantastic performance in the then-upcoming James Gray romance Two Lovers, Phoenix famously swore he had given up acting for a rap career. He grew a beard and spent the next 12 months convincing the world it was true: brawling at Miami nightclubs; performing a disastrous set in Vegas, described by Rolling Stone as "nothing short of a train wreck"; talking only about hip-hop during press for Two Lovers, his "final" film; and, of course, rattling David Letterman by refusing to play along with the grin-and-charm publicity circuit. (Letterman arguably deserved it: When Phoenix first appeared on his show in 1998, he was so gawky that Letterman compared him to Pauly Shore.)

More than 5 million viewers saw Phoenix's mumbling stunt live on Late Night, and millions more caught it on YouTube. Only a fraction saw the reason behind it: the Casey Affleck mockumentary I'm Still Here, a tricky and disconcertingly deadpan dissection of the media machine, which had devoured Phoenix's music-career mistakes like junk food. (Typical talking-head snark: "Is it a hoax? Do we care?")

Even audiences who saw the final film left confused. It was, Affleck conceded, "a hard movie to watch," even as he praised Phoenix for giving "a terrific performance...the performance of his career." The film made only $408,983 at the box office, even as bearded Phoenix became a national joke. Ben Stiller mocked him at the Oscars, blundering around the stage while presenting the cinematography award and sticking his chewing gum on the crystal podium.

The experiment hinged on people knowing the real Joaquin Phoenix wasn't a whiny, idiot egotist who snorted coke and sniffed hookers' butts. But people didn't.

"When I was writing 'BYE! GOOD' on my hand, I thought people would be like, 'Okay, this is not happening. This can't be real,'" Phoenix muses. "But whenever I did that really over-the-top stuff, some people would doubt it, but then some people would go for it more."

Was he surprised people really believed he was a shuffling doofus who didn't comb his hair?

"Well, I haven't combed my hair right now," he chuckles. "And I do have a great shuffle."

The root of I'm Still Here is Phoenix's frustration with fame. That feels true. His parents raised him to be a star, but also raised him to see through the bullshit.

Arlyn and John Phoenix (then surnamed Bottom) met hitchhiking in California in 1969. The nomadic hippies quickly built a family, adding to their brood every two years: River was born in Oregon, Rain in Texas and, in 1974, Joaquin was born in Puerto Rico, where the family had followed the controversial Children of God cult, which discouraged TV and newspapers and promoted all-ages sex. (River later confessed to Details magazine that he lost his virginity at four.) Two more sisters, Liberty and Summer, followed.

Joaquin was raised in Caracas, where his father was the cult's "archbishop of Venezuela and the Caribbean." Despite Dad's fancy title, the kids supported the family by dancing for pocket change on the streets while their parents gradually distanced themselves from the group. When Joaquin was 3, the same year the family unanimously became vegetarian, they fled to Miami on a cargo ship.

By five, Joaquin's world had changed radically: The family resettled in L.A., where Arlyn was secretary to the head of casting at NBC. (At home, the only TV channel they had was PBS.) To celebrate their resurrection, they gave themselves a new last name: Phoenix.